This invention relates generally to pollution control systems and, more particularly, to a pollution control system for the removal of sulfur oxides from flue gases and the reduction of the sulfur oxides to sulfur.
It is known in the field of atmospheric pollution control to use an adsorptive process for the desulfurization of flue gases in which the sulfur-containing material is adsorbed in the porous system of an activated carbonaceous material. In one such process, adsorption is carried out in a gas-solid contacting device in which the flue gases are contacted with activated char, and sulfur dioxide in a diluted form in the gas stream passing through the activated char is adsorbed and oxidized to sulfuric acid by the oxygen and water vapor present in the gas stream. Other acid gases, such as nitrogen oxides, are similarly adsorbed, and particulate matter entrained in the gas stream is filtered by passage of the stream through the activated char.
The acid-laden or saturated char is then usually thermally regenerated in a desorption vessel, or the like, by a process in which the sulfur-containing material is chemically changed in form, resulting in the decomposition of sulfuric acid to sulfur dioxide and water, whereby a portion of the carbonaceous adsorbent is oxidized to carbon dioxide. The by-product of the regeneration process is a gas stream containing 20-30% by volume of sulfur dioxide, which is directed to an off-gas treatment facility for further processing.
In an off-gas treatment system developed by the Foster Wheeler Corporation, the assignee of the present application, and disclosed in U.S. Patent Application Ser. No. 635,497, filed Nov. 26, 1975, the gas stream from the desorption vessel is directed to a reactor in which most of the sulfur dioxide is reduced to gaseous elemental sulfur, which is then condensed and stored in liquid or solid form. In either form, the elemental sulfur offers a non-polluting and easily-handled, salable product.
In the foregoing technique, a portion of the activated char is chemically consumed in the regeneration process and another portion becomes physically worn to a size which is ineffective in the reduction process. Consequently, the technique requires an additional supply of activated char to replace the quantity consumed. Since the activated char is the most expensive commodity consumed in the process, it would be economically desirable to either reduce the consumption of this commodity or to provide a less-expensive substitute to replenish the quantity consumed.